1. Field Of The Invention
The present invention relates to a cementing head apparatus, and more particularly to containers for releasing balls and darts, and to associated swivels for permitting rotation during the cementing operation.
2. Description Of The Prior Art
One type of cementing system which is commonly used in the completion of offshore wells is that known as a subsurface release cementing system. In a subsurface release cementing system, the cement plugs themselves are hung off in the upper end of the casing near the ocean floor. Devices such as balls and darts are released from a plug container or cementing head located at the floating drilling rig. The balls or darts fall downward through drill pipe to engage the cementing plugs hung off in the casing head, and to cause those cementing plugs to be released and to then flow down through the casing with the cement.
One such system is shown in U.S. Pat. No. 4,624,312 to McMullin, assigned to the assignee of the present invention.
Another such system is shown in U.S. Pat. No. 3,616,850 to Scott. As shown in the Scott patent, the devices launched from the upper head to engage and release the cementing plugs typically include a ball for releasing the bottom cementing plug and a dart for releasing the top cementing plug.
It is also known to construct the cementing head in what is known as a "lift-through" design, wherein the entire weight of the drill pipe which is hung below the drilling platform is supported through or lifted through the structure of the cementing head. One such system is that known as the Nodeco system which is shown in Exhibit A filed herewith. The Nodeco system utilizes a lifting sub having a loading bore defined therethrough and having an upper cap with a rod extending downward therefrom and extending through the loading bore. The Nodeco system also utilizes a swivel below the cementing head.
Various designs of heavy-duty swivels are also known to the art. One example is the Bowen workover swivel manufactured by Bowen Tools, Inc., of Houston, Texas, as shown at page 1293 of Volume 1 of the 1982-83 Composite Catalog of Oilfield Equipment and Services. The Bowen swivel includes three bearings operating in an oil bath.